Display surfaces in image display devices such as liquid crystal displays (LCDs) or cathode ray tube display devices (CRTs) are required to reduce the reflection of light emitted from an external light source such as a fluorescent lamp and thus to enhance the visibility of the image. To meet this demand, an optical laminate (for example, an antireflective laminate) comprising a transparent object and a transparent film having a low refractive index covering the surface of the transparent object for lowering the reflectance has been provided to reduce the reflection from the display surface of the image display device and thus to improve the visibility.
For example, from the viewpoint of contamination resistance of display face of an image display device, an antistatic layer is often provided in an optical laminate. For example, Japanese Patent Laid-Open No. 94007/2004 proposes an antireflective optical laminate comprising a light transparent base material and an antistatic layer and a hardcoat layer provided in that order smoothly on the surface of the light transparent base material.
In the antireflective laminate comprising layers having a large refractive index difference stacked on a light transparent base material, however, interface reflection and interference fringes often occur at an interface of mutually superimposed layers. In particular, it is pointed out that, at the interface between the light transparent base material and the antistatic layer, interference fringes occur resulting in deteriorated visibility of images.
On the other hand, the present inventors have produced an optical laminate comprising an antistatic layer in a concave-convex form and have examined optical properties of the optical laminate. As a result, it was found that the haze value of the optical laminate is somewhat increased although interference fringes can be effectively prevented. Further, although interference fringes can be prevented, in an optical laminate comprising a hardcoat layer having a proper thickness (0.8 to 20 μm) provided on concaves and convexes in the antistatic layer, optical concave-convex deformation attributable to the antistatic layer sometimes stays on the outermost surface. For this reason, it was found that, in general, flattening of the outermost surface of the optical laminate as a final form approximately to a level of the outermost surface of an optical laminate in which only a hardcoat layer has been stacked, is very difficult. As a result, it was confirmed that, when an optical laminate comprising an antistatic layer having concaves and convexes is incorporated in an image display device, passage of transmitted light from within the device through the nonflat outermost surface causes shining dazzling derived from the optical concave-convex deformation.
Further, imparting concaves and convexes in the antistatic layer requires a multi-stage process and further requires an apparatus or the like for concaves and convexes. This poses a problem such as increased production cost. The above various problems can be solved by the formation of proper concaves and convexes in curing the composition for an antistatic layer.
Further, since the antistatic layer is generally provided between a light transparent base material and a hardcoat layer, in general, the antistatic agent in the antistatic layer is in a densely aggregated state. That is, when the antistatic agent is in the form of ultrafine particles which are present discretely or as aggregates, the fine particles or aggregates per se should be in contact with each other in any site. On the other hand, when the antistatic agent is an organic electrically conductive composition, the formation of a film of a homogeneous antistatic layer is necessary for the development of antistatic properties.
So far as the present inventors know, however, up to now, any optical laminate comprising an antistatic layer has not been proposed in which the presence of an antistatic agent in an antistatic layer in a satisfactorily dispersed state without being aggregated in the layer while maintaining the antistatic properties, or alternatively the formation of the antistatic agent as a cracked heterogeneous film rather than a homogeneous film on one side of an antistatic layer in which an organic electrically conductive composition as an antistatic agent is imparted and formed, can effectively prevent interface reflection and interference fringes at the interface between the antistatic layer and the light transparent base material, can realize flattening as in an optical laminate in which only a hardcoat layer is provided without any antistatic layer on the outermost surface, and can eliminate dazzling, a problem involved in the image display screen.